Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
A286 Lock Washers
A286 lock washers are spring-action washers placed under hex nuts or bolt heads to maintain residual clamping force as the joint relaxes from thermal cycling, vibration or settling. TorqBolt manufactures four primary A286 lock washer types: split-ring (helical spring per DIN 127 / ISO 7090), Belleville disc spring (conical disc per DIN 6796), external-tooth (radial teeth per DIN 6797 / IFI-101), and internal-tooth (inward teeth per DIN 6798 / IFI-101). Stamped or laser-cut from A286 sheet (AMS 5895) or plate (AMS 5525), then solution-treated and aged to develop spring-back. Sizes M3-M30 metric and #4-1/2 inch. Note: at temperatures above ~540 °C, lock washers lose spring-back due to material yield — for high-temperature anti-vibration use A286 self-locking nuts instead. See parent A286 washers, sister flat washers, and the canonical chemical composition, heat treatment.
About A286 Lock Washers
A286 lock washers achieve their anti-loosening function through stored spring energy — when the joint clamps, the washer compresses; if the joint relaxes (thermal contraction, settlement, vibration micro-creep), the washer spring-back maintains residual clamping force. Each lock washer is blanked from A286 sheet, formed to the required spring profile (helical for split-ring, conical for Belleville, tooth-stamped for serrated), then solution-treated 1650 °F and aged 1325 °F × 16 hours to develop the gamma-prime precipitation that gives A286 its spring properties. Hardness 277-302 HBW post-aging. The non-magnetic austenitic matrix makes A286 lock washers compatible with same-material A286 bolt-and-nut joints at temperatures from -196 °C cryogenic to ~540 °C (above which spring-back diminishes).
A286 Lock Washer Types & Standards
TorqBolt produces four primary A286 lock washer configurations:
- Split-ring lock washer (DIN 127 / ISO 7090) — Helical spring single-coil — most common general-purpose lock washer. M3-M30 sizes. Note: split-ring effectiveness is debated; modern engineering prefers Belleville or self-locking nut.
- Belleville disc spring (DIN 6796) — Conical disc washer with high spring constant — used in stacks for high-preload retention. Aerospace and high-precision applications. M3-M30.
- External-tooth lock washer (DIN 6797 / IFI-101) — Radial teeth on outer perimeter — bites into both nut bearing face and joint surface. Best lock for radial-load joints.
- Internal-tooth lock washer (DIN 6798 / IFI-101) — Inward-facing teeth — bites into bolt-head bearing face. Used where outer-tooth would damage decorative finish.
- Internal-external tooth (DIN 6797 / 6798 combined) — Radial teeth on both inner and outer perimeter — maximum locking action for safety-critical joints.
A286 Lock Washer Sizes & Reference
| For bolt size | Split-ring (DIN 127) | Belleville (DIN 6796) | Tooth (DIN 6797) | Inner ⌀ | Outer ⌀ | Thickness |
|---|---|---|---|---|---|---|
| M3 | ✓ | ✓ | ✓ | 3.1 mm | 6.2 mm | 0.8 mm |
| M4 | ✓ | ✓ | ✓ | 4.1 mm | 7.6 mm | 0.9 mm |
| M5 | ✓ | ✓ | ✓ | 5.1 mm | 9.2 mm | 1.2 mm |
| M6 | ✓ | ✓ | ✓ | 6.1 mm | 11.8 mm | 1.6 mm |
| M8 | ✓ | ✓ | ✓ | 8.1 mm | 14.8 mm | 2.0 mm |
| M10 | ✓ | ✓ | ✓ | 10.2 mm | 18.1 mm | 2.2 mm |
| M12 | ✓ | ✓ | ✓ | 12.2 mm | 21.1 mm | 2.5 mm |
| M16 | ✓ | ✓ | ✓ | 16.2 mm | 27.4 mm | 3.5 mm |
| M20 | ✓ | ✓ | — | 20.2 mm | 33.6 mm | 4.0 mm |
| M24 | ✓ | ✓ | — | 24.5 mm | 40.0 mm | 5.0 mm |
A286 Lock Washers Manufacturing Process
Every a286 lock washers TorqBolt ships traces back to a vacuum-induction-melted plus vacuum-arc-remelted (VIM-VAR) ingot meeting AMS 5731 / 5732 chemistry. The complete process route:
- Sheet input + blanking: AMS 5895 aged sheet (typical) or AMS 5525 sol-treated plate. Sheet thickness selected per washer-thickness table. Punch-press blanks washers from sheet.
- Forming (split-ring): Helical spring profile formed in coining die — single-coil with sloped ends. Spring-rate set by sheet thickness and helix angle.
- Forming (Belleville disc): Conical disc formed in compression die — conical angle 6-8° typical for DIN 6796.
- Forming (toothed): Radial teeth stamped on outer (DIN 6797) or inner (DIN 6798) perimeter using specialized perforating die.
- Solution treatment (if not pre-aged sheet): Vacuum heat-treat 1650 °F (899 °C) per AMS 5737 / ASTM A453 Class A. AMS 5895 sheet may already be aged — verify input condition.
- Precipitation aging: 1325 °F (718 °C) for 16 hours, air-cool. Develops gamma-prime Ni₃(Ti,Al) — gives A286 its spring properties.
- Spring-rate verification: Sample from each lot tested on spring-rate test fixture per DIN 6796 / IFI-101 — measure compressed deflection at specified load.
- Passivation: Pickle + HNO₃ rinse + passivate per ASTM A967 Type II.
- Inspection + bulk pack: 100 % visual + dimensional check; bulk pack 500 / 1000 / 2500 pcs per drum.
A286 Lock Washers Inspection & Certification
Each lot ships with a signed inspection certificate. Aerospace orders are released with AS9102 first-article inspection per AS9100D AQMS. Industrial orders default to EN 10204 type 3.1. Variant-specific inspection scope:
- Inner ⌀ and outer ⌀ verified by ring gauge per DIN 127 / 6796 / 6797 / 6798.
- Thickness 100 % gauged with calibrated calliper or micrometer.
- Spring-rate sample testing per DIN 6796 / IFI-101 — compressed deflection at specified load.
- Hardness sample 1 per 500 washers per ASTM E384.
- Magnetic permeability < 1.005 per ASTM A342 on every aerospace lot.
- Visual inspection for blanking burr, edge crack, surface scratch.
- AS9102 first-article on aerospace lots.
- Salt-spray ASTM B117 96-hour for passivated lots.
A286 Lock Washers Torque & Assembly Practice
Lock washers compress under bolt preload — they do NOT add to the bolt clamping force calculation. The bolt is torqued to its specified preload; the lock washer compresses and stores spring energy. As the joint relaxes (thermal cycling, settling), the lock washer spring-back maintains residual clamping. CRITICAL: lock washers stack only one per joint side — multiple stacked lock washers cause unpredictable spring-rate behaviour and unreliable preload. Above ~540 °C the A286 lock washer loses spring-back due to material yield — for high-temperature anti-vibration use jam-nut pair or all-metal self-locking nut instead.
A286 Lock Washer Applications by Industry
Lock washers retain joint preload under thermal cycling and vibration — applications:
- Aerospace electronic enclosures: Internal-tooth lock washers under SHCS heads on avionics rack and instrumentation enclosures — positive lock against vibration without nylon insert (which decomposes above 120 °C).
- Industrial gas turbines < 540 °C: Belleville disc springs in stacks under combustor casing flange bolting — maintains preload through thermal cycle. Above 540 °C use jam-nut or self-locking instead.
- Marine engine hardware: Split-ring (DIN 127) on diesel-engine mounting bolts, exhaust-system clamping. Salt-spray corrosion resistance + non-magnetic.
- Power generation auxiliary: External-tooth (DIN 6797) on transformer terminal bolts, switchgear connections — bites into bus-bar surface for electrical and mechanical retention.
- Aerospace landing gear: Belleville disc spring stacks on landing-gear pivot bolts where preload retention through cyclic loading is critical.
- Cryogenic LNG / hydrogen: Belleville and split-ring lock washers under LNG valve bolts and hydrogen storage manifold flanges. Spring-back retention down to -196 °C.
Governing Standards & Material Specifications
Every A286 fastener is released against the applicable industry standard. EN 10204 type 3.1 mill certificates ship with every order. See the consolidated A286 AMS / ASTM specifications hub.
| Authority | Specification | Coverage |
|---|---|---|
| ASTM | A453 grade 660 Cl. A/B/C/D | High-temperature bolting material |
| ASTM | A638 grade 660 Type 1/2 | Forged bolting stock |
| AMS | 5731 | Bar / forging — solution-treated |
| AMS | 5732 | Bar / forging — solution-treated and aged |
| AMS | 5737 | Bar — sol-treated and aged (precision) |
| UNS | S66286 | Material designation |
| DIN | 1.4980 / X5NiCrTiMoVB25-15-2 | European designation |
| EN | 10204 3.1 / 3.2 | Mill / third-party-witness certification |
A286 Lock Washers vs Alternative Materials
Engineers compare A286 against three alternatives: A286 vs Inconel 718, A286 vs 17-4 PH, and A286 vs Waspaloy. A286 is the cost-performance leader for non-magnetic precipitation-hardening service in the 540-700 °C envelope. See A286 equivalent grades.
How to Specify A286 Lock Washers
A complete a286 lock washers callout should include all eight elements: material spec, heat-treatment condition, dimensional standard, size, thread tolerance class, surface finish, marking, inspection certificate. Example callout:
Lock washer, DIN 127 split-ring, A286 / UNS S66286, ASTM A453 grade 660, AMS 5895 aged, ID 8.1 mm, OD 14.8 mm, thickness 2.0 mm, passivated, EN 10204 3.1.
A286 Lock Washers — Frequently Asked Questions
What is the difference between a flat washer and a lock washer?
Flat washer: simple flat ring, distributes bearing pressure. See A286 flat washers. Lock washer: spring-action washer (split-ring, Belleville, or toothed) that maintains residual clamping force when joint relaxes. Use both: flat washer for bearing distribution + lock washer for vibration retention.
Are split-ring lock washers actually effective?
Engineering opinion is divided. Studies (NASA, Junker test) show split-ring washers are LESS effective than self-locking nuts or Belleville stacks for vibration retention. Modern aerospace and high-criticality engineering prefers self-locking nuts (MS 21043 / NAS 1291) or Belleville disc-spring stacks. Split-ring is acceptable for low-criticality industrial applications.
What's the difference between Belleville disc and split-ring washers?
Belleville disc: conical disc with very high spring constant — stores significant energy in small deflection, retains 90 % preload through thermal cycle. Split-ring: helical spring with low spring constant — stores less energy, retains ~60 % preload. Belleville for safety-critical and high-cycle joints; split-ring for low-cost industrial.
Can A286 lock washers be used above 540 °C?
No. Above ~540 °C A286 yields and loses spring-back; the lock washer compresses permanently and stops providing anti-loosening function. For high-temperature anti-vibration use jam-nut pair (DIN 936) or all-metal self-locking nut (DIN 6927 / MS 21043 / NAS 1791).
Are A286 lock washers magnetic?
No. Magnetic permeability < 1.005 verified on every aerospace lot per ASTM A342. Compatible with same-alloy A286 bolt-and-nut joints in instrumentation, MRI, and electromagnetic-sensitive applications.
Can I stack multiple lock washers under one nut?
No. Stacked lock washers cause unpredictable spring-rate behaviour and unreliable preload. Use ONE lock washer per joint side. For higher spring force use a Belleville disc stack (multiple Belleville washers in series or parallel arrangement) — this is properly engineered.
Which lock washer for an aerospace application?
Aerospace primary structure: typically NOT lock washers — use self-locking nuts (MS 21043 / NAS 1291) or castle nuts with cotter pins instead. Lock washers used on aerospace SECONDARY: avionics enclosures, accessory gearbox covers — internal-tooth (DIN 6798) preferred.
Can a lock washer replace a flat washer?
No. Lock washer compensates for joint relaxation only — it does NOT distribute bearing pressure across a wider area. Use BOTH: flat washer (closer to joint) for bearing distribution, lock washer (under nut/bolt-head) for retention. Single-washer use is acceptable only on hardened steel joint surfaces where bearing damage is not a concern.
What's the spring rate of a Belleville washer?
Per DIN 6796: highly variable by size and material thickness. M16 A286 Belleville: ~ 50,000 N/mm spring rate, max deflection 0.4 mm at 20,000 N load. Used in stacks (parallel for higher load, series for greater deflection) to match joint preload requirements.
Why TorqBolt for A286 Lock Washers
Three reasons aerospace and gas-turbine OEMs place a286 lock washers orders with us:
- Vertically integrated supply — VIM-VAR melt, in-house cold heading + thread rolling + vacuum heat-treatment.
- Aerospace AQMS — AS9100D-certified factory in Mumbai with published quality manual.
- Lead time discipline — 4-6 weeks standard, 8-12 weeks aerospace custom.
Three decades of fastener manufacturing experience; current certifications: ISO 9001:2015, AS9100D, PED 2014/68/EU, NORSOK M-650 QTR.
Recent A286 Lock Washers Order Patterns
Recurring lock-washer applications: DIN 127 split-ring M6/M8 on aerospace electronic enclosure bolting, DIN 6796 Belleville disc M10/M12 on landing-gear pivot bolts, DIN 6797 external-tooth M5 on transformer terminals, and Belleville stacks for nuclear-grade reactor-vessel bolting M30.
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